1. Field of the Invention
The invention relates to the field of wax emulsions and mixtures for addition to settable gypsum formulations, and more particularly to the field of such mixtures and emulsions for making gypsum wallboards having good strength properties.
2. Description of Related Art
Gypsum wallboard is used for forming interior and exterior walls of many building structures. The structure of the wallboard typically includes a gypsum composition which is generally prepared as a slurry composition, which is placed between two liners and set. Such wallboard gypsum compositions may be standard wallboard formulations or made to be water-resistant through, for example, the use of various wax emulsions. Some of the more common commercial water-resistant wax emulsions involve use of particular wax components (which may include a single wax, or more typically, a blend of waxes), saponifying agent(s), emulsifier(s), stabilizer(s) and other additives.
Of growing importance in the wallboard industry is the ever-increasing cost of manufacture of wallboard with respect to the rising cost of formulation components as well as increasing energy costs. For example, it is known in the art that manufacturing methods for formation of building products like gypsum wallboard that use emulsions in formation of the finished products, typically require a drying step or steps that consume energy. Thus, it would be beneficial to manufacture gypsum wallboard (standard and water-resistant) if the drying energy could be reduced for cost savings, particularly when energy demands are growing for manufacturers. Components, time and steps required in manufacture are also a concern, as is the quality of the resulting wallboard.
With respect to the manufacture of water-resistant wallboards, U.S. Pat. No. 5,437,722 describes a water-resistant gypsum composition and wax emulsion therefor, which includes a paraffin hydrocarbon having a melting point of about 40° C. to 80° C., about 1 to 200 parts by weight montan wax per 100 parts of the paraffin hydrocarbon, and about 1 to 50 parts by weight polyvinyl alcohol per 100 parts of the paraffin hydrocarbon. The use of montan wax in the wax emulsion for water-resistant wallboard has been very effective and provides excellent performance. Other water-resistant formulations based on natural waxes other than montan (such as carnauba and bees wax) and/or synthetic waxes (such as Fischer-Tropsch wax) have been used as well as alternative water-resistant wax formulations. Most such formulations provide good water-resistance in gypsum wallboard formulations. However, some waxes typically used for such emulsions are in limited supply and/or are very expensive. Further, while strong water-resistance can be achieved, it would be desirable to achieve good water resistance properties in gypsum wallboard, while lowering the cost of components, increasing supply and/or reducing manufacturing costs.
There have been attempts to enhance physical properties of wallboard, however, many such proposed enhancements are expensive and/or complex and/or involve additional manufacturing steps such that the process becomes less economical. Many boards are strengthened with fibrous reinforcement, such as woven mats, but getting the slurry to adhere to the mat is typically an issue. In some instances extra films and/or mats are laminated onto the wallboard during or after its formation to increase the impact strength and other mechanical properties of the wallboard.
For example, WO 2010/025207 A1 describes a durable and strong gypsum board having woven porous mats, such as mats made from fibers and held together with a binder such as a urea, a dense slurry layer penetrating the porous mats which may have a thermoplastic pre-coating thereon. A core of slurry is also provided. The plastic layer provided on the mats is to mechanically adhere to polymer additives in the dense slurry layers surrounding the mats. External coating layers are also provided to the wallboard. The disclosure describes the mats as providing strength to the board. Polymer additives suggested to bond with the mats and increase strength are polyvinylidene chloride, polyvinyl chloride, and similar polymers, as well as functionalized styrene butadiene latex and silane compounds which may also serve as stabilizers.
U.S. Pat. No. 7,615,504 also teaches a fiber-mat reinforced board wherein the board can have a core of gypsum or Portland cement. This patent also teaches additional sizing, coatings and binders for the mats. The additional plastic coating on the mat may include various polymers including polyvinyl acetate, polyvinyl chloride and other polyvinyl copolymers.
U.S. Pat. No. 7,048,794 teaches addition of various starch compounds including substituted starch and polysaccharides to enhance strength in gypsum boards.
U.S. Pat. No. 6,406,799 teaches a paperless wallboard having a primer for providing a smoother surface and improved surface characteristics, wherein the primer incorporates a water-based system that heat cures to improve the surface of the board. The primer can include a latex that is an aqueous emulsion of a film-forming polymer having a glass transition temperature of 10-40° C., such as acrylic polymers and copolymers, polyvinyl acetate/acrylate copolymers, ethylene vinylchloride/vinyl acetate polymers and others.
Polymer additives are also provided to other building materials aside from gypsum compositions for strength and/or flexibility. For example, U.S. Publication No. 2002/0195025 A1 teaches a powder composition for addition as a rheological additive for water retention and thixotropic purposes in cement-containing mortar compositions or “cement-free” mortar compositions, in place of or in addition to cellulosic materials typically used, wherein the powder includes a copolymer of methacrylic acid and methacrylic esters, a dispersant and a polymer powder redispersible in water, including a variety of vinyl-based copolymers including ethylene vinyl acetate copolymers. Such additives are asserted to improve rheological properties without negatively impacting curing of the mortar.
Accordingly, there is a need in the art for compositions and methods that improve the properties of gypsum wallboard while preferably also keeping the costs of manufacturing including reducing energy costs at or lower than standard levels, and that avoids adding complex process steps or expensive components.